1. Field of the Invention
The present invention relates to a toner for an electrostatic charge development for use in an electrophotography and a method for producing the toner.
2. Description of the Related Art
An image forming method for visualizing image information via an electrostatic charge image by an electrophotographic method is now utilized in various fields. In recent years, with development of digitalization or a high-grade image processing technique, a technique for obtaining a higher quality image has been required.
Regarding such requirement for the high quality image, It has been in progress to bring the toner for the electrostatic charge development into that having a small size and a uniform particle size distribution. In a conventional knead-grinding method, there is a limitation in bring it into that having the small size. With reference to bring it into that having the uniform particle size distribution, even when the toner is allowed to pass through a classification step, it can not sufficiently be responded to bring the image into that having a high quality.
Further, a consideration to the environment, a low energy consumption, a low cost and a long period of life time are required for the toner for the electrostatic charge development. As measures for attaining these features, from the standpoint of a fixation technique, oilless fixing for the long period of life time, and a low-temperature high-speed fixation for the low energy consumption and the low cost can be mentioned. As for methods for attaining these measures, a method in which a releasing agent such as a wax is contained in the toner such that the toner itself has a releasing effect has ordinarily been performed.
However, it is a present situation in which, in the conventional knead-grinding method, it is difficult to control a structure of the releasing agent and control an amount to be added in a same manner as in the case of bringing the toner into that having a high quality. Accordingly, the aforementioned measures hardly become practical attaining measures.
In recent years, as a method for actively controlling a structure of the toner for the electrostatic charge development, JP-A-63-282752 and JP-A-6-250439 have proposed a method for producing a toner by an emulsion-polymerization-aggregation method. In JP-A-63-282752 and JP-A-6-250439, a production method of a toner in which a resin dispersion liquid is prepared by an emulsion-polymerization method, a colorant dispersion liquid in which an colorant is dispersed in a solvent is prepared and, then, both dispersion liquids are mixed to form an aggregate having a particle diameter corresponding to that of the toner and, thereafter, the thus-formed aggregate is heated, to thereby be coalesced. In this method, a shape can be controlled to some extent and improvements of a charging property and durability can be attained. However, since an inner structure of the toner becomes approximately uniform, there remain problems in a releasing property of a fixing sheet at the time of fixing and a fixing property under a low-temperature high-speed condition.
Then, in JP-A-5-61239, a toner for oilless fixing which contains a large amount of releasing agent component in the toner has been proposed. However, when a large amount of releasing agent is added, although a releasing property is improved to some extent, a binder component and the releasing agent exhibit compatibility therebetween and, then, oozing of the releasing agent can not stably and uniformly be performed and, accordingly, a releasing stability can not be obtained. Further, dispersibility of each material inside the toner comprehensively affects fixing properties to a great extent, such as, an adhesion property of the aforementioned fixed image to paper, a releasing property from a fixing roll, a folding resistance after the fixing, a gloss and an OHP transparency.
As for methods for improving dispersibility of the releasing agent, for example, in JP-A-2-105163, a method in which a property to be contained and an oozing property of the releasing agent are both improved by actively incorporating a resin having a polar group has been proposed. However, although this method has improved the oozing property and the property of containing the releasing agent to some extent, little effect in controlling a position of the releasing agent within the toner or improving dispersibility of the colorant is obtained and, as a result, the fixing property can not fully be improved.
Further, in JP-A-9-073187 and JP-A-10-161338, focusing on a structure of a releasing agent in a toner, the toner in which a ratio of a major axis to a minor axis of a wax in the toner is defined has been described. Although such method as described in JP-A-9-073187 and JP-A-10-161338 has improved an oozing property of the releasing agent at the time of fixing to some extent in a same manner as in the case described above and improved a fixing performance, there is little effect in efficiency and an oozing speed and, also, there is no description on thermal characteristics of the releasing agent. Accordingly, it is difficult to sufficiently correspond to the low-temperature high-speed fixing or the oilless fixing.